The present invention relates to the donor doping of conjugated backbone polymers such as polyacetylene.
Conjugated backbone polymers, such as polyacetylene, are known which can be intercalated by alkali metal cations chemically or electrochemically. In chemical doping, the polymer is reacted with an electroactive organometallic compound of an alkali metal such as an alkali metal naphthalide (e.g. lithium naphthalide or sodium naphthalide). Examples of such processes are contained in A. G. MacDiarmid et. al. and A. J. Heeger Syn. Metals, Vol. 1, pp. 101-118 (1980). Donor doped polyacetylene is especially described in U.S. Pat. No. 4,204,216 to Heeger et al. (1980).
In electrochemical doping, the polymer (e.g. polyacetylene) is contacted with a salt solution (e.g. lithium perchlorate in propylene carbonate) and electrons are fed into the polymer and withdrawn from the counter electrode, causing the polymer to become negatively charged and the cation of the salt (e.g. lithium cations) to migrate into the polymer as a counterion. Such electrochemical doping can be used as a charging mechanism for a battery (see, e.g., U.S. Pat. No. 4,321,114 to MacDiarmid et al. (1982)). Such batteries are difficult to break in, however, if neutral polymer is initially used for the anode since the undoped polymer has a high internal resistance which hampers the initial introduction of electrons. Ways to render the electrode less resistive in the undoped state are by either filling the polymer with a conductive substance (e.g., graphite powder) or by initially chemically doping the polymer. Both methods introduce extraneous substances (e.g. naphthalene or graphite) into the battery, however, which add weight and, in some cases, complicating side reactions (such as self-discharge of the battery moderated by naphthalene) without increasing the active mass of the electrode.